Integrated circuitry fabricated on semiconductor chips generates heat during normal operation. If the heat generated becomes excessive or the heat generated is not effectively removed, the integrated circuit device can malfunction or fail. In other words, the reliability of the integrated circuit device may be compromised if the integrated circuit device overheats. There are many ways to remove heat from an integrated circuit device, for example, by placing the integrated circuit device in a cool spot in the enclosure or using a liquid-cooled plate connected to a refrigerated water chiller. In general, the amount of heat generated by the integrated circuit device, the integrated circuit device package configuration and the expected lifetime of the product combine with many other factors determine the optimum heat removal scheme.
The interface between the integrated circuit device and the heat dissipation device used to cool the integrated circuit device may be a factor in designing a thermal solution. More specifically, microscopic air gaps (e.g., caused by surface non-uniformity) between an integrated circuit device package and a heat sink attached to the integrated circuit device package's surface may affect or degrade thermal performance. Typically, the degradation in thermal performance increases as the operating temperature increases. The surface variability induced by varying surface roughness may be reduced by using interface materials appropriate to the package type. However, it is difficult, if not impossible, to completely eliminate the surface variability.
The development of faster and denser circuit technologies and smaller packages which are accompanied by increasing heat fluxes at the chip and package levels complicate the problem. Although significant advances have been made in air cooling techniques to manage increased heat fluxes, it has long been recognized that significantly higher heat fluxes are better accommodated through the use of liquid cooling.
FIG. 1 shows an electronic device 100 having a cavity-up design. A flip-chip 106 is bonded to a substrate 102 via flip-chip bumps 108. A lid 110, which can be multi-component or one component is attached to substrate 102 via adhesive 112. Lid 110 provides mechanical structure strength to the device. A cold plate 116 is attached to lid 110 with an adhesive 120.
Cold plate 116 is constructed of a cap 116a and a base 116b. Base 116b includes fins 116c and cap 116a includes an inlet 122 and an outlet 124. Cap 116a is attached to base 116b through an adhesive 121, forming channels 116d. Electronic device 100 may be coupled to a printed circuit board (PCB) via Ball Grid Array (BGA) balls 104.
In FIG. 1, the thermal path for dissipating heat generated by flip-chip 106 includes adhesive 114, lid 110 and adhesive 120. Each junction/interface (e.g., between flip-chip 106 and lid 110, between lid 110 and cold plate 116) causes a junction temperature which is undesirable because junction temperatures increase the impedance of the thermal path, thus decrease thermal dissipation efficiency.
In some instances, where thermal requirements cannot be met with the added junction temperature caused by the adhesive between the lid and the adhesives, the lid may be eliminated all together and a cold plate directly attached to the silicon substrate. Although the resulting structure eliminates the junction temperature caused by the lid, the elimination of the lid also eliminates the mechanical strength provided by the lid, resulting in a weak structure.